1. Field of the Invention
The invention relates to sound systems, and more specifically to surround sound systems adapted to home and automotive systems.
2. Background of the Invention.
Sound systems may include one or more channels from which the sound may be perceived. Single channel sound systems produce a non-dimensional sound that does not allow the listener to localize the sound. With two-channel reproduction of sound, localization may occur, but horizontal localization may be poor unless the listeners are centered between the speakers. Even so, the difference between a two-channel reproduction of sound and single-channel reproduction may be perceived and appreciated throughout the room.
In practice, most listeners may not be precisely centered between the loudspeakers. Presumably two channels are used because both localization and room sound reproduction are enhanced with more loudspeakers and more discrete channels. The two-channel loudspeaker system in a relatively non-reverberant room may create a realistic spatial field when the listeners face a particular direction. Typically, the sound field may seem spacious to the listeners when the listeners face forward. Conversely, the sound field may collapse when the listeners face to a side.
A common standard for the production and playback of sound recordings with more than two discrete channels uses five discrete channels and an additional band limited low frequency channel. Recordings are mixed by assuming the listener is located at the center of an array of loudspeakers, placing three speakers in front of the listener and two speakers behind the listener. The front speakers are referred to as left front, center, and right front. The rear speakers are referred to as left surround and right surround.
Such 5.1 surround sound mixing may be adequate if the listener is positioned in exactly the center of a symmetric loudspeaker array. Such positioning, however, is almost never achieved. The average listener moves around, and the average home sound system is rarely arranged exactly as desired. When the listener moves away from the center of the speaker array, e.g. moves away from the listening point, if the original recording does not use the center speaker, the front sound image may collapse. The front sound image may collapse to the nearest loudspeaker, similar to the way the sound image collapsed with the two-channel stereo.
Likewise, in an automotive environment, the listener is not positioned in the exactly the center of a symmetric loudspeaker array. In an automobile there is no listener in the center of the space. Because of the seating restrictions in the automobile, every listener is close to at least one of the loudspeakers. In an automobile the sound appears to come from the speaker nearest to the listener, and the spatial reproduction is poor or non-existent.
In addition, if the center channel is used in the recoding, sound from the center channel, that is output from a speaker located in the front and center of the automobile, will appear to come from the right of the driver and the left of the passenger. In this listening environment, the sound from the center channel will not be heard by passengers located in the rear of the automobile.
In addition, in the past, many sound mixers have used only two front channels, and do not use the center channel of a 5.1 surround sound system. These mixers tend to produce recordings that are basically “quadraphonic” by distributing equally into the left front and right front channels important sounds that are intended to sound from the center of a sound-image, and ignore the discrete center channel. There exists a reasonably large catalogue of such quadraphonic recordings from the 1970's and 1980's that are slowly becoming available as 5-channel recordings, but lack programming information for the center channel.
Thus, for at least the above identified reasons relating to listening environment and products, listener position, and sound recordings, there exists a need for a system to improve the localization and the spatial illusion of the sound to produce a more robust sound.